To be fair, that isn't that many guns. If he's moving from OH to PA, he'd be moving his stuff. I can say, last time I moved, there were plenty more in transport than that! If those other 3 are out of direct reach, and unloaded, I doubt that is a crime to transport the weapons if he's legally allowed to possess them in general. The issue with the unpermitted carry is because that one firearm was concealed. Cops will almost never just 'let it slide' on a potential gun charge, even if there's an understandable reason for it. The charge may end up dropped, but they will still generally confiscate it and do an initial charge. The drugs make it a more damning situation, but if it's low weight for personal use, I would assume a decent lawyer will be able to get the gun charge dropped. The registration is nothing, and if it's light weight on the weed, that may get provisionally dropped as well.
It could always be something more, but looking at the circumstances from very far away, it sounds way worse than it is.